This invention relates to an improved fermentation medium and process for making an aliphatic polycarboxylic acid using said medium.
Long-chain alpha, omega-dicarboxylic acids, i.e., those having a carbon number of 9 or higher, are used as raw materials in the synthesis of a variety of chemical products and polymers.
Diacids with carbon numbers greater than four are currently produced almost exclusively by nonbiological conversion processes. These types of chemical processes for the production of diacids have a number of limitations and disadvantages. Each process is restricted to the production of diacids of specific carbon chain lengths, based on the starting material used. For example, the dodecandioic acid process begins with butadiene, therefore the products of this reaction process are limited to acids with chain lengths in multiples of four. In addition, the processes are based on nonrenewable petrochemical feedstocks, and the multireaction conversion process produces unwanted byproducts which result in yield losses, heavy metal wastes, and nitrogen oxides which must be destroyed in a reduction furnace.
Biological conversion processes for the production of diacids have a number of potential advantages relative to the existing non-biological conversion processes. Primary among these is the use of renewable feedstocks as starting materials and the ability to produce-the diacid without the generation of hazardous chemical byproducts which necessitate costly waste disposal processes.
Another important advantage achieved by using a biological process is that such a process can easily be adapted to produce a wide variety of diacids using the same biocatalyst and the same equipment. Because current organic chemical syntheses are suited to the production of only a single diacid, the sythesis of several different diacids would require the development of a new synthetic scheme for each diacid. On the other hand, a yeast biocatalyst can be used to produce diacids of varying lengths using the same equipment, media and protocols merely by providing a different substrate to the yeast.
U.S. Pat. No. 6,004,784, the entire contents of which is hereby incorporated by reference, discloses a semi-synthetic fermentation medium which employs corn steep liquor and brewers yeast extract in order to reduce the cost of conventional fermentation media which contain expensive, highly standardized yeast extracts and yeast nitrogen bases.
The problem associated with the use of such inexpensive substitutes is many fold. They result in a fermentation broth having significant odor emissions when sparged with air. Particulate matter, especially combined with high levels of bacteria, contained in corn steep liquor and crude yeast extracts make them difficult to sterilize and contribute to the bioburden on media sterilization equipment. These subsitutes also contain many unmetabolizable components that contribute to color and color stability problems which need to be attended to using additional purification steps with their incumbent product losses. The selection of these substitutes, while lowering media cost, add additional process costs. Consequently, there remains a need for a low-cost, biofermentation medium which provides nutrients to support growth of the yeast biocatalysts permitting high specific productivity of polycarboxylic acids, polyols, and polyhydroxy acids.